Controlling a hydraulic hybrid vehicle powertrain having an internal combustion engine and a hydraulic pump/motor

Abstract

A motor vehicle powertrain system according to this invention controls the magnitudes of torque produced by multiple power sources that drive the vehicle wheels. The system includes a source of pressurized fluid, and a pump/motor driveably connected to the wheels, which is driven in a motoring mode by fluid from the fluid source and has a variable volumetric displacement that changes in response to displacement of the accelerator pedal. An engine, driveably connected to the wheels, includes a throttle that opens and closes in response to displacement of the accelerator pedal. A controller controls operation of the engine and pump/motor such that they produce torque at various magnitudes. The system determines a magnitude of desired wheel torque, a maximum available engine wheel torque, a maximum available pump/motor wheel torque, a difference in magnitude between the desired wheel torque and the maximum available pump/motor wheel torque, operates the pump/motor as a motor such that the pump/motor produces a magnitude of wheel torque that is equal to the lesser of the desired wheel torque and the maximum available pump/motor wheel torque, and operates the engine such that the engine produces a magnitude of wheel torque that is equal to the lesser of the maximum available engine wheel torque and the difference in torque magnitude.

1. In a motor vehicle powertrain that includes an engine having a displaceable throttle, and a variable displacement pump/motor driven by fluid from a source of pressurized fluid, the engine and pump/motor being driveably connected to wheels of the vehicle, a method for controlling magnitudes of torque produced by the engine and the pump/motor comprising the steps of:
 determining a magnitude of desired wheel torque; 
 determining a maximum available engine wheel torque; 
 determining a maximum available pump/motor wheel torque; 
 determining a difference in magnitude between the desired wheel torque and the maximum available pump/motor wheel torque; 
 operating the pump/motor as a motor such that the pump/motor produces a magnitude of wheel torque that is equal to the lesser of the desired wheel torque and the maximum available pump/motor wheel torque; and 
 operating the engine such that the engine produces a magnitude of wheel torque that is equal to the lesser of the maximum available engine wheel torque and said difference in magnitude. 
 
   
   
     2. The method of  claim 1 , wherein the engine throttle opens and closes in response to displacement of an accelerator pedal, and the step of determining a magnitude of desired wheel torque further comprises:
 establishing a first relation of desired wheel torque to a range of vehicle speed for various positions of the accelerator pedal; and 
 using the current accelerator pedal position and the current vehicle speed to determine the desired wheel speed from said first relation. 
 
   
   
     3. The method of  claim 1 , wherein the step of determining a maximum available engine wheel torque further comprises:
 establishing a second relation of engine wheel torque to a range of engine speed for a wide open engine throttle condition; 
 determining a current engine speed; and 
 using the second relation to determine a magnitude of wheel torque the engine could produce at the current engine speed if the engine throttle were wide open. 
 
   
   
     4. The method of  claim 1 , wherein the pump/motor includes an inlet connected to the source of pressurized fluid and an outlet, and the step of determining a maximum available pump/motor wheel torque further comprises:
 establishing a third relation of pump/motor wheel torque at maximum displacement to a range of differential pressure between the inlet and the outlet, and pump/motor operating efficiency; 
 determining a current magnitude of said differential pressure and efficiency current engine speed; and 
 using the third relation to determine a magnitude of wheel torque the pump/motor would produce if the pump/motor were operating as a motor and producing maximum displacement. 
 
   
   
     5. The method of  claim 1 , wherein the step of determining a difference in magnitude further comprises:
 determining a difference in magnitude between the desired wheel torque and the pump/motor wheel torque that would be produced by the pump/motor while operating at maximum displacement of the pump/motor. 
 
   
   
     6. The method of  claim 1 , wherein the step of operating the pump/motor further comprises:
 using fluid contained in the source of pressurized fluid to drive the pump/motor; 
 adjusting the displacement of the pump/motor such that the pump/motor produces a magnitude of wheel torque that is equal to the lesser of the desired wheel torque and the maximum available pump/motor wheel torque; and 
 transmitting to the wheels the torque produced by the pump/motor. 
 
   
   
     7. The method of  claim 1 , wherein the step of operating the pump/motor further comprises:
 using fluid contained in the source of pressurized fluid to drive the pump/motor; 
 adjusting the displacement of the pump/motor such that the pump/motor produces a magnitude of wheel torque that is equal to the lesser of the desired wheel torque and the pump/motor wheel torque that would be produced by the pump/motor while operating at maximum displacement of the pump/motor; and 
 transmitting to the wheels the torque produced by the pump/motor. 
 
   
   
     8. The method of  claim 1 , wherein the step of operating the engine further comprises:
 adjusting an engine operating parameter such that the engine produces a magnitude of wheel torque that is equal to the lesser of the maximum available engine wheel torque and said difference in magnitude; and 
 transmitting to the wheels the torque produced by engine. 
 
   
   
     9. The method of  claim 8 , wherein the step of adjusting an engine operating parameter further comprises:
 adjusting a member of the group consisting of an engine throttle position, a rate of engine airflow, an engine ignition timing, an engine air-fuel ratio, and an engine fuel flow. 
 
   
   
     10. The method of  claim 1 , wherein the step of operating the engine further comprises:
 adjusting an engine operating parameter such that the engine produces a magnitude of wheel torque that is equal to the lesser of said difference in magnitude and the engine wheel torque the engine could produce at a current engine speed if the engine throttle were wide open; and 
 transmitting to the wheels the torque produced by engine. 
 
   
   
     11. A motor vehicle powertrain system for controlling magnitudes of torque produced by multiple power sources that drive the vehicle wheels, comprising:
 a source of pressurized fluid; 
 an engine driveably connected to the wheels, including a throttle that opens and closes in response to displacement of the accelerator pedal, 
 a pump/motor driveably connected to the wheels, driven in a motoring mode by fluid from the fluid source, having a variable volumetric displacement; and 
 a controller for determining a magnitude of desired wheel torque, determining a maximum available engine wheel torque, a maximum available pump/motor wheel torque, a difference in magnitude between the desired wheel torque and the maximum available pump/motor wheel torque, and for operating the pump/motor as a motor such that the pump/motor produces a magnitude of wheel torque that is equal to the lesser of the desired wheel torque and the maximum available pump/motor wheel torque, and operating the engine such that the engine produces a magnitude of wheel torque that is equal to the lesser of the maximum available engine wheel torque and said difference in magnitude. 
 
   
   
     12. The system of  claim 11  further comprising a displaceable accelerator pedal, and wherein:
 the engine throttle opens and closes in response to displacement of the accelerator pedal; and 
 the controller further is accessible to a first relation of desired wheel torque to a range of vehicle speed for various positions of the accelerator pedal, and the controller uses the current accelerator pedal position and the current vehicle speed to determine the desired wheel speed from said first relation. 
 
   
   
     13. The system of  claim 11  wherein the controller further is accessible to a second relation of engine wheel torque to a range of engine speed for a wide open engine throttle condition, the controller uses the second relation to determine a magnitude of wheel torque that the engine could produce at the current engine speed if the engine throttle were wide open. 
   
   
     14. The system of  claim 11 , wherein:
 the pump/motor includes an inlet connected to the source of pressurized fluid and an outlet; and 
 the controller further is accessible to a third relation of pump/motor wheel torque at maximum displacement to a range of differential pressure between the inlet and the outlet, and pump/motor operating efficiency, the controller determines a current magnitude of said differential pressure and efficiency current engine speed, and the controller uses the third relation to determine a magnitude of wheel torque the pump/motor would produce if the pump/motor were operating as a motor and producing maximum displacement.